The goal of becoming an official flavour is the correct route to go down in my opinion. That will get you a whole host of extra goodness for free, above and beyond somewhere to host your ISOs. For example, inclusion in the ISO tracker QA platform:

I don’t get it. You have to be a member to have edit access to the wikis. I’ll PM cariboo. Maybe I got expired;)

I think I found what is happening here. When you applied for Ubuntu Membership you gave another Launchpad account, right? This one: https://launchpad.net/~twocamels
You have to use this account to gain the Ubuntu People space. Upload an ssh key and wait a few hours to be activated. Then try again, this time sftp://twocamels@people.ubuntu.com

The only test I can think of now is if you do a hard install, see if it will exit and complete properly. You may have to wait a few extra seconds at the end until it notifys to remove USB and press enter to restart.

No special modification. Everything upstream that is developed on 18.04 will roll into this installation.

Thanks to everyone here!! We all did this together. What an awesome community in action!